Technical Field
The present invention relates to a fluororesin tube, and particularly, to a tube of polytetrafluoroethylene (referred to as “PTFE” below) as a material of the tube, having a thin thickness.
Background Art
A PTFE tube is suitably used in a material and the like of a medical catheter because of excellent characteristics such as chemical resistance, non-adhesiveness, and low friction. In an endovascular surgery, a catheter is inserted into a blood vessel and a lesion site in a blood vessel is removed, treated, or the like. Because a burden of a patient is small, such an endovascular surgery becomes the mainstream. It is necessary that a catheter used for such a purpose is percutaneously inserted toward the inside of a body, and a tip end of the tube is caused to reach a lesion site via a blood vessel. In addition, the catheter requires, for example, straightness which represents straightly traveling in a blood vessel and operation transmissibility which represents transmission of an operation of a practitioner who performs treatment. In order to satisfy the demand, the catheter is configured by stacking layers which have different characteristics. The inner diameter of the catheter is preferably as large as possible, because it is necessary that, for example, a jig is inserted or a chemical liquid is injected into the catheter. In addition, the outer diameter of the catheter is preferably small in order to reduce the burden on a patient. Thus, each of the layers constituting the catheter is required to be as thin as possible.
As one method of manufacturing a catheter tube, there is a method in which a core wire such as a copper wire is coated with PTFE, an exterior resin layer is formed on the resultant of the coating, then the core wire is pulled out, and thereby a catheter tube is obtained (for example, see Patent Document 1). As a method of coating a core wire with PTFE, there are a method (referred to as “a dipping method” below) of coating a core wire with a PTFE dispersion and sintering the resultant of the coating, and a method of performing direct paste extrusion forming on the core wire. In addition, there is a method of performing coating by covering a core wire with a PTFE tube. At this time, the PTFE tube is extended in a state where the core wire is inserted into the PTFE tube, the diameter thereof is reduced, and thus the PTFE tube adheres to the core wire. Thus, the tube requires an elongation for performing extension and a tensile strength for withstanding extension.
Since PTFE has a very large melt viscosity, a PTFE tube is generally formed by not melt extrusion forming but paste extrusion forming (for example, see Patent Document 2). However, in the paste extrusion forming, it is difficult to form a tube having a thin thickness. In a case of forming a PTFE tube having a thin thickness, the dipping method is much used (for example, see Patent Document 3). However, a tube formed by the dipping method has a problem of weak tensile strength.
For example, Patent Document 4 discloses a method in which the paste extrusion forming is performed, and then the tube is extended in a longitudinal direction so as to reduce the thickness, in order to obtain a tube which has a thin thickness and a large tensile strength.